1. Field of the Invention
The present invention is directed to a mattress, and, in particular, to a mattress in which the softness or hardness of the mattress can be changed or adjusted if desired.
2. Related Art
A typical conventional mattress of the type wherein an elasticity of the mattress depends on the property of a fluid which is sealed in a bag is disclosed in Japanese Utility Model Laid-open Print No.Sho.63(1988A.D.)-1451 or Japanese Patent Laid-open Print No.Hei.2(1990A.D.)-15 6906. In the conventional mattress, an amount of fluid is sealed in a bag on which a person lays. For adjusting the elasticity or firmness of the bag according to his/her taste, the amount of the fluid in the bag may be changed. In detail, if harder elasticity and softer elasticity are required, the fluid is supplied to and drained from the bag, respectively. Suppling fluid into the bag causes the bag to inflate to increase the elasticity of the bag, while draining fluid from the bag makes the bag deflate to decrease the elasticity of the bag.
In the foregoing conventional structure for adjusting the elasticity of the bag, the mattress includes an outside vessel that stores the fluid to be supplied to the bag or drained from the bag. In addition, the outside vessel has a meter or an instrument that indicates the quantity of fluid supplied to and drained from the bag. Moreover, sometimes a pump is needed to automatically transfer the fluid between the bag and the outside vessel.
However, the outside vessel, the meter or the instrument, and the pump provide a complex arrangement in the vicinity of the mattress. Particularly, if the outside vessel is positioned below the bag, the height of the resultant mattress becomes extremely high, thereby lowering the practically or utility of the mattress.